There are historical depictoions from the 9th centrury but it was more likely a personal flag.
The left one one THIS mosaic and HERE a rendition of the same.
Then there is the Oriflamme Flag but this is also quite questionable because it's a modern association.
This would be your proposal, but after transforming it to the 16x16 pixel format, the flag itself would be 14x11, there will be not much left.
